Wet etching is a technique in which a metal layer, which is not covered by a photoresist, on a surface area of a substrate is etched using an etchant, to form desired metal wires. The capability of wet etching directly affects product yield.
When a substrate placed in an etching apparatus is etched through the wet etching process, etchant sprayed on the substrate flows away from periphery of the substrate, such that the replacement rate of the etchant in the peripheral portion of the substrate is high while that in the central portion of the substrate is low (i.e., liquid accumulation effect), resulting in that the periphery of the substrate is etched quickly while the central portion of the substrate is etched slowly (i.e., etching capability is not uniform). As such, it is apt to cause defects such as width of a metal wire is not uniformly distributed, thereby affecting product yield. As the development of large-sized substrate and the increase in thickness of metal film layer, the phenomenon of the non-uniform etching capability due to the liquid accumulation effect is more severe.